Commit 47a8aad1 authored by Catalin Marinas's avatar Catalin Marinas Committed by Will Deacon
Browse files

arm64: gcs: Honour mprotect(PROT_NONE) on shadow stack mappings 



vm_get_page_prot() short-circuits the protection_map[] lookup for a
VM_SHADOW_STACK mapping since it uses a different PIE index from the
typical read/write/exec permissions. However, the side effect is that it
also ignores mprotect(PROT_NONE) by creating an accessible PTE.

Special-case the !(vm_flags & VM_ACCESS_FLAGS) flags to use the
protection_map[VM_NONE] permissions instead. No GCS attributes are
required for an inaccessible PTE.

Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Fixes: 6497b66b ("arm64/mm: Map pages for guarded control stack")
Cc: stable@vger.kernel.org
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Reviewed-by: default avatarDavid Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 8a85b313

arch/arm64/mm/mmap.c

+5 −1
Original line number Diff line number Diff line
@@ -91,7 +91,11 @@ pgprot_t vm_get_page_prot(vm_flags_t vm_flags) 


	/* Short circuit GCS to avoid bloating the table. */

	if (system_supports_gcs() && (vm_flags & VM_SHADOW_STACK)) {

		/* Honour mprotect(PROT_NONE) on shadow stack mappings */

		if (vm_flags & VM_ACCESS_FLAGS)

			prot = gcs_page_prot;

		else

			prot = pgprot_val(protection_map[VM_NONE]);

	} else {

		prot = pgprot_val(protection_map[vm_flags &

				   (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]);